7,510 research outputs found
Forecasting Intraday Time Series with Multiple Seasonal Cycles Using Parsimonious Seasonal Exponential Smoothing
This paper concerns the forecasting of seasonal intraday time series. An extension of Holt-Winters exponential smoothing has been proposed that smoothes an intraday cycle and an intraweek cycle. A recently proposed exponential smoothing method involves smoothing a different intraday cycle for each distinct type of day of the week. Similar days are allocated identical intraday cycles. A limitation is that the method allows only whole days to be treated as identical. We introduce an exponential smoothing formulation that allows parts of different days of the week to be treated as identical. The result is a method that involves the smoothing and initialisation of fewer terms than the other two exponential smoothing methods. We evaluate forecasting up to a day ahead using two empirical studies. For electricity load data, the new method compares well with a range of alternatives. The second study involves a series of arrivals at a call centre that is open for a shorter duration at the weekends than on weekdays. By contrast with the previously proposed exponential smoothing methods, our new method can model in a straightforward way this situation, where the number of periods on each day of the week is not the same.Exponential smoothing; Intraday data; Electricity load; Call centre arrivals.
Resistive Magnetohydrodynamic Equilibria in a Torus
It was recently demonstrated that static, resistive, magnetohydrodynamic
equilibria, in the presence of spatially-uniform electrical conductivity, do
not exist in a torus under a standard set of assumed symmetries and boundary
conditions. The difficulty, which goes away in the ``periodic straight cylinder
approximation,'' is associated with the necessarily non-vanishing character of
the curl of the Lorentz force, j x B. Here, we ask if there exists a spatial
profile of electrical conductivity that permits the existence of zero-flow,
axisymmetric r esistive equilibria in a torus, and answer the question in the
affirmative. However, the physical properties of the conductivity profile are
unusual (the conductivity cannot be constant on a magnetic surface, for
example) and whether such equilibria are to be considered physically possible
remains an open question.Comment: 17 pages, 4 figure
Entanglement between the future and past in the quantum vacuum
We note that massless fields within the future and past light cone may be
quantized as independent systems. We show that the vacuum is an entangled state
of these systems, exactly mirroring the known entanglement between the
spacelike separated Rindler wedges. We describe a detector which exhibits a
thermal response to the vacuum when switched on at t=0. The feasibility of
experimentally detecting this effect is discussed.Comment: 4 pages, 1 figur
Dual mode laser velocimeter
Described is a laser Doppler velocimeter (LDV) which is capable of operating with a small focus diameter for analyzing fluid flows at low velocity with high spatial resolution, or with a larger focus diameter to measure fluid flows at higher velocities accurately. More particularly, this is an LDV in which a simple reversal of a lens pair will allow it to operate in the two focus diameter modes
Optical coherence tomography with a Fizeau interferometer configuration
We report the investigation of a Fizeau interferometer-based OCT system. A
secondary processing interferometer is necessary in this configuration, to
compensate the optical path difference formed in the Fizeau interferometer
between the end of the fibre and the sample. The Fizeau configuration has the
advantage of 'downlead insensitivity', which eliminates polarisation fading. An
optical circulator is used in our system to route light efficiently from the
source to the sample, and backscattered light from the sample and the fibre end
through to the Mach-Zehnder processing interferometer. The choice of a Mach-
Zehnder processing interferometer, from which both antiphase outputs are
available, facilitates the incorporation of balanced detection, which often
results in a large improvement in the Signal-to-Noise ratio (SNR) compared with
the use of a single detector. Balanced detection comprises subtraction of the
two antiphase interferometer outputs, implying that the signal amplitude is
doubled and the noise is well reduced. It has been discerned that the SNR drops
when the refractive index variation at a boundary is small. Several OCT images
of samples (resin, resin + crystals, fibre composite) are presented
Fiber-optic chemical sensing with Langmuir-Blodgett overlay waveguides
Fiber-optic chemical sensing has been demonstrated with a side-polished single-
mode optical fiber, evanescently coupled to chemically sensitive Langmuir-
Blodgett (LB) overlay waveguides. The sensors exhibit a channel-dropping
response centered on a wavelength that is dependent on the thickness and the
refractive index of the overlay waveguide. It has been shown that pH-sensitive
organic dyes proved to be suitable materials fur the formation of an overlay
waveguide whereas LB deposition provides the required thickness control. A
theoretical model of the sensor response, based on the Kramers-Kronig relations
and phase matching of the guided modes within the optical fiber and overlay
waveguide, shows good agreement with experimental results
Benchmarking the Advanced Search Interfaces of Eight Major WWW Search Engines
This research project was designed to benchmark the performance of the advanced search interfaces of eight of the major World Wide Web (WWW) search engines, excluding the meta engines. A review of the literature did not find any previous benchmarking studies of the advanced interfaces based on quantitative data. The research was performed by fifty-two graduate students of library and information studies (LIS) on three campuses of the University of North Carolina (UNC) as a class research project for course LIS 645, Computer-Related Technologies in Library Management. The class was offered by the Department of Library and Information Studies at UNC Greensboro through the North Carolina Research and Education Network (NC-REN). The LIS students selected Altavista, Excite, Go/Infoseek, Google, Hotbot, Lycos, Northernlight, and Yahoo for comparative study
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